In the field of offshore oil and/or gas production pipeline systems are normally used. In particular, at offshore oilfields, subsea pipelines are used to transport the multiphase mixture of oil, gas and water from producing wells to the processing facilities on the land. Several kilometers of pipeline run on the seabed for this purpose.
The pipeline is provided with a coating for isolating the pipeline from the contact with sea water, in order to prevent corrosion.
Along the pipeline a plurality of sensors are normally installed inside the coating of the pipeline, for remotely monitoring the conditions of the pipeline itself and promptly detect any damage or problem. For example, PH sensors may be provided for indirect measurement of corrosion or pressure sensors for monitoring any excessive pressure drop along the pipeline which may be due to a leak. Mass flow rate sensors may also be installed for detecting leaks. In any case, sensors have normally to be installed in contact with the pipeline, i.e. inside the pipeline coating, in order to properly function.
The sensors distributed along the pipeline needs power to do the provided measurements and communicate the results along the pipeline. The battery packages are placed outside the coating of the pipeline. This will assure that batteries could be changed, for example when exhausted, without removing any part of the coating. Battery packages cannot be mounted on the pipeline before reeling, due to the diameter on the reels used for storage of pipeline. The reels needs pipeline with uniform diameter and the presence of battery packages would violate these requirements. Therefore, but battery packages have to be mounted on the pipeline as the last job before the pipeline is installed. This job is normally done on the vessel which installs the pipeline in a subsea installation, thus making the installation process longer.
Another drawback is the fact that, even if these batteries can last for 20-25 years, they are nevertheless subject to run off of charge, needing the exhausted battery to be replaced with a new one. The maintenance operation for replacing the battery in a subsea environment may be a difficult operation, in any case involving time and costs to be performed.
In addition, an electrical connection has to exist between the batteries and the electronics/sensors which are present inside the coating. This means that, when installing the sensors on the pipeline, an electrical connection has to be provided for each sensor. The electrical connection has to pass through the coating, in order to connect it, during the later installation phase, with the battery package providing power. The connection between the electronic inside the coating on the pipeline and the battery package is a weak point in the assembly for each sensor node distributed along the pipeline, for example a point through which sea water can reach the pipeline.
A further drawback of the presence of the battery packages outside the pipeline is the fact that the distributed battery packages increases the diameter of the pipeline but only on some spots, i.e. the spots where a sensor is present, giving a lesser smooth pipeline which makes the piping installation process more complicated.
A possible solution for avoiding the use a battery package in a subsea device is described in DE 10 2008 056087, where the use of optical fibres guided on a pipeline for the purpose of measuring temperature and/or pressure is described. The optical fibres comprise individual sensors on the pipeline in a decentralized manner and can be supplied by an external underwater Bragg unit to which an accumulator is associated. Such accumulator receives energy from an inductive converter inductively couple to an electrical underwater cable.